The i70/i70S MFIDs are neither designed to report battery voltage sensed from power drawn from the SeaTalkng backbone nor from engine systems (the latter is alternator voltage). These MFIDs are designed to report battery voltage sensed from a NMEA 2000 battery monitoring device such as Maretron's DCM100 direct current / battery monitor. Are you interfaced a NMEA 2000 battery monitoring device(s) to your system's battery(ies)?